The invention relates to a process for determining an estimated value for the noise level n of a background noise which is superimposed on an acoustic useful signal, in particular a human speech signal, transmitted via a telecommunications (=TC) system. The invention further relates to computer programs and devices for supporting and executing such a process, in particular suitable server units, signalling equipment, processor modules and programmable gate array modules. The invention is based on a priority application DE 100 52 626.8 which is hereby incorporated by reference.
Processes for the noise estimation of background noises are known. For example noise estimators are used in which, for the estimation of the noise level of a signal, the value of the signal averaged in a short time interval (SAM=short average magnitude) is used.
In other processes the so-called MAM (=medium average magnitude) value of an input signal is measured in longer time intervals. To achieve a reliable estimation result, measurement times up to 500 ms are required. Often the MAM value also simulates too high a noise level compared to the actual noise level.
In general the value of the noise level of a signal is of great importance for many signal processing algorithms as threshold value or control value. The reliability and time response of a noise estimator have a large influence on the attainable quality of a signal processing algorithm. This applies in particular to the field of speech recognition for improving the recognition rate, to the field of echo suppression and to noise reduction. Application areas for noise estimators are for example switching systems, conference equipment as well as conventional telephones or hand-held devices.
A disadvantage of known estimating processes is the relatively long response of the averaging in the noise estimator. Especially in the case of speech activity with only short speech pauses at time intervals of <100 ms, often the time is insufficient to detect the “noise base”.
In accordance with the ITU-T guide line G.168, so-called composite signals are used consisting of a sequence of signal bursts with a pause time of approximately 100 ms. Here again, exact noise estimation is not possible with the previously known processes.
Another problem associated with the noise threshold is noise updating under environmental conditions which change over time as performed in successful speech level estimation. The estimated noise value thus fluctuates within specific, often relatively large, limits.